Hi Claudio,

  I think there has been a misunderstanding. I agree with you (and I
think also Marco) that LSN is definitely a component to consider in
this process. We will come up with an alternate proposal which
considers LSNS either today or tomorrow. ;)

Thanks,
Gabriele
--
 Gabriele Bartolini - 2ndQuadrant Italia
 PostgreSQL Training, Services and Support
 gabriele.bartol...@2ndquadrant.it | www.2ndQuadrant.it


2014-08-04 20:30 GMT+02:00 Claudio Freire <klaussfre...@gmail.com>:
> On Mon, Aug 4, 2014 at 5:15 AM, Gabriele Bartolini
> <gabriele.bartol...@2ndquadrant.it> wrote:
>>    I really like the proposal of working on a block level incremental
>> backup feature and the idea of considering LSN. However, I'd suggest
>> to see block level as a second step and a goal to keep in mind while
>> working on the first step. I believe that file-level incremental
>> backup will bring a lot of benefits to our community and users anyway.
>
> Thing is, I don't see how the LSN method is that much harder than an
> on-disk bitmap. In-memory bitmap IMO is just a recipe for disaster.
>
> Keeping a last-updated-LSN for each segment (or group of blocks) is
> just as easy as keeping a bitmap, and far more flexible and robust.
>
> The complexity and cost of safely keeping the map up-to-date is what's
> in question here, but as was pointed before, there's no really safe
> alternative. Nor modification times nor checksums (nor in-memory
> bitmaps IMV) are really safe enough for backups, so you really want to
> use something like the LSN. It's extra work, but opens up a world of
> possibilities.


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